Final answer:
The P wave represents the depolarization wave received from the SA node through the atria.
Step-by-step explanation:
The portion of the electrocardiogram that represents the depolarization wave received from the sinoatrial (SA) node through the atria is the P wave. The P wave represents the depolarization and contraction of the atria as they pump blood into the ventricles. It is a small, upward deflection on the ECG.